Phosphoric acid is used according to the art to protonate cationic resins primarily for use as or in cathodically depositable paint binders. See, for example, U.S. Pat. No. 4,304,703, DE-OS No. 22 65 195, U.S. Pat. No. 3,954,588, or DE-OS No. 27 53 595. In all of the aforesaid disclosures the phosphoric acid is set free through discharge on electrodeposition. In the prior art, epoxy resins modified with phosphoric acid were characterized by a content of free acid groups whereby the resins could be rendered water-soluble through salt formation with bases. It is evident that such resins are not suitable for the use in cationic resins.